The devout Muslim, wearing a skull cap, wiped away tears several times in the brief footage which he filmed sitting in a car.
Police reported multiple deaths in attacks on two crowded mosques during Friday prayers in Christchurch, where Williams played for the Crusaders earlier in his career.
"Inshallah (God willing) everyone who's been killed today... you guys are all in paradise," he added.
"Just deeply, deeply saddened that this would happen in New Zealand.
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